1. Field of the Invention
The invention relates to an infrared heater, and more particularly to a reflecting hood specially designed for an irradiating unit to improve the heat reflecting efficiency by avoiding radiant heat from being reflected to its infrared tube, so as to extend the life expectancy of the infrared tube and enhance the irradiating range of the heater and the evenness of heat energy.
2. Description of the Related Art
Electric heater is a type of electric appliance, which converts the electrical energy to thermal energy. In order to increase the thermal efficiency of electric heater, the lamp tube as a source of heating radiation has been evolved to the high-powered infrared tube. However, though the thermal energy of electric heater and the light energy of illuminating appliance, both have lamp tube respectively, the function and the requirement differ completely. For example, part of the emitting light of the illuminating appliance is radiated by the tube directly, and most of the other part will concentrate in certain angle after reflection by the reflecting cap to achieve the required focusing brightness.
However, in addition to the required relative high power, the lamp tube as a source of heating radiation of electric heater demands the thermal energy on effective range of proliferation, so that the distribution of thermal energy would be better.
Conversely, if the method which is employed in the illuminating appliance and through which the heat is concentrated in a particular narrow area is taken, not only will the purpose of warming of surrounding space fail to achieve, but also the thermal energy focusing is easy to be formed in the illuminated area due to the concentration of thermal energy like the light beam, thereby making the exposed person uncomfortable.
Secondly, the French scientist Fermat proposed the principle that should be applied on the light transmission way. It is the well-known Fermat theorem. In other words, the light transmission process must comply with the principle of least time. Thus, this principle, which the light should comply with after reflection, is known as the law of reflection. We illustrate law of reflection with FIG. 1. When the light emits from n medium to n′ medium, some light returns at interface surface MN′ back to n medium. This phenomenon is known as reflection. The plane that is comprised of S, B, and P is called as incident plane. SB light ray is called as incident light. Meanwhile, BP-light ray is reflective light and MN′ light ray is known as normal line. The angle between the incident light and normal line is called as incident angle θi. The angle between reflective light and normal line is called as reflection angel θr. The law of reflection can be summarized into the following three points:
(1) The incident light, reflective light and the normal line are on incident plane together
(2) The incident light, reflective light are on both sides of the normal line
(3) The incident angle is equal to the reflection angel, θi=θr.
In addition, as shown in the FIG. 2 and FIG. 3, the reflection caps of the current electric heater are shown in the two figures. In accordance with the above described Fermat theorem, no matter whether the arc-shaped reflection cap (11) or the  shaped reflection cap (12) are applied, it can be concluded that the upward radiation heat from the upper half of center (S) of the heating source of the infrared lights tubes (10) creates incident light {right arrow over (SB)} and reflective lights {right arrow over (BP)}, {right arrow over (BB′P)} after the reflection by the reflection cap. The reflective light (heat) concentrates in the middle area, as shown in FIG. 8. Furthermore, the incident light (SA) upon the center (S) of the heating source focuses on the light tube (10) after reflection. Besides, the waste of heating source, the reflected heat in this area has extremely high temperature, which leads to an adverse influence to the life span of the infrared lights tubes (10). Moreover, most of the reflection caps of current electric heaters are made by bending a metal plate. When the heating effect of incident light {right arrow over (SA)} and reflective light {right arrow over (AS)} continues, the accumulated heat cannot be released efficiently. After a long-termed use, light reflection caps (11) or (12) are easily deformed, or even bent. Therefore, the application is not yet very ideal.